Fluid distribution systems often implement encoders to measure quantities of distributed fluid. These encoders generally mate to a fluid metering device, by way of example, to a shaft of a piston meter, and operate to calculate the amount of distributed fluid by measuring the number of cycles or rotations of the piston meter. Traditional encoders may be mechanically disabled, preventing the fluid distribution system from accurately measuring the quantity of dispensed fluid. For example, a thief may mechanically disconnect the encoder from the piston meter in a fuel distribution system while leaving the encoder electronically connected to the system. Such a modification would allow the continued output of fuel. However, with the encoder-piston arrangement disconnected, the system would fail to accurately detect the volume of fuel distributed, as well as the corresponding payment owed therefore.
Magnetic-based encoders typically operate by mechanically affixing a magnet to the rotatable shaft and having a sensor positioned relative to the magnet-shaft for measuring a change in the magnetic field (e.g. a change in the direction of the magnetic field) caused during rotation. Certain tampering techniques intended to defeat this arrangement include (in addition to removing the encoder discussed above) introducing, a powerful magnetic field into proximity with this arrangement. In particular, by introducing a high flux density magnetic field, such as by activating an electromagnet near the fuel distribution system, one may disrupt the magnetic sensor of the encoder from accurately reading the change in direction of the magnetic field caused by the rotating magnet, and thus may avoid paying the fair value for the distributed fuel.
Designs for a fuel distribution system that avoid vandalism, tampering, or theft may be limited by the operating environment of the system. In particular, encoders are generally located within the cabinet of a fuel distribution system. These systems are designed to be highly ventilated to allow leaked or spilled fuel to efficiently evaporate. This ventilation, however, allows for continued presence of fuel vapors around the encoders, limiting viable design options. For example, designs may avoid switches due to the risk of an electrical arc that may cause fuel vapors to ignite. Similarly, designs may avoid various mechanical interactions due to the risk of sparks caused by friction igniting fuel vapors.
Alternative tamper-resistant encoders adapted to operate in a highly combustible environment are desired.